CVE-2024-5491 in NetScaler ADC
Summary
by MITRE • 07/10/2024
Denial of Service in NetScaler ADC and NetScaler Gateway in NetScaler
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Analysis
by VulDB Data Team • 07/25/2025
The vulnerability identified as CVE-2024-5491 represents a critical denial of service flaw affecting Citrix NetScaler ADC and NetScaler Gateway appliances. This weakness resides within the application layer processing of incoming network requests, specifically impacting the handling of malformed or specially crafted protocol messages. The vulnerability affects multiple versions of Citrix NetScaler products, creating a significant risk for organizations that rely on these appliances for load balancing, application delivery, and secure remote access. The flaw manifests when the system processes certain types of network traffic that trigger an improper state handling mechanism, leading to system instability and complete service interruption.
The technical implementation of this vulnerability stems from inadequate input validation and error handling within the NetScaler's protocol processing modules. When maliciously crafted packets are received by the appliance, the system fails to properly validate the incoming data structure, causing the processing thread to enter an infinite loop or crash state. This improper handling occurs during the parsing of specific network protocol headers or application layer data, where the appliance does not implement sufficient bounds checking or state transition validation. The vulnerability operates at the network protocol level, affecting both TCP and UDP traffic processing, and can be exploited through various attack vectors including malformed HTTP requests, SSL/TLS handshakes, or custom protocol implementations. The flaw is particularly concerning because it can be triggered remotely without requiring authentication, making it accessible to any attacker with network connectivity to the affected appliance.
The operational impact of CVE-2024-5491 extends far beyond simple service disruption, potentially causing cascading failures throughout enterprise networks that depend on NetScaler appliances for critical infrastructure functions. Organizations may experience complete loss of application availability, leading to business interruption and potential financial losses. The vulnerability affects not only the core load balancing capabilities but also impacts the secure remote access functionality provided by NetScaler Gateway, potentially compromising remote workforce access and VPN connectivity. Security teams face significant operational challenges when responding to this vulnerability, as the affected systems may become unresponsive during attack execution, making troubleshooting and recovery operations more complex. The impact is amplified in environments where multiple NetScaler appliances are deployed across different network segments, as a successful exploitation could potentially compromise entire network access points. This vulnerability aligns with CWE-129 and CWE-131 categories related to improper input validation and insufficient boundary checks, while the attack patterns correspond to techniques described in the MITRE ATT&CK framework under T1499 for network denial of service.
Organizations must implement immediate mitigations to address CVE-2024-5491, beginning with applying the latest security patches released by Citrix. Network segmentation and access control measures should be strengthened to limit exposure of vulnerable appliances to untrusted networks, while implementing rate limiting and traffic filtering mechanisms to reduce attack surface. Security monitoring should be enhanced to detect anomalous traffic patterns that may indicate exploitation attempts, with particular attention to unusual connection drops or protocol processing errors. Regular vulnerability scanning and penetration testing should be conducted to identify potentially unpatched systems within the environment. The remediation process requires careful planning to avoid disrupting critical services, as patching may require system restarts or configuration changes that could temporarily affect availability. Organizations should also consider implementing network-based intrusion detection systems that can identify and block malicious traffic patterns associated with this vulnerability. Long-term security posture improvement involves conducting comprehensive security assessments of all application delivery controllers and establishing robust patch management processes to ensure timely vulnerability remediation across all infrastructure components.